ANRV360-ES39-13 ARI 21 August 2008 20:29 Single-species management: population abundance is assessed for an individual species on the basis of natural mortality, anthropogenic (fishing) mortality, and population reproductive rates 262 Crowder et al.

No abstract

No abstract

Loggerhead sea turtles Caretta caretta have been found to damage crab pots and reduce catch of blue crabs Callinectes sapidus in North Carolina sounds. In response, crabbers have avoided fishing at locations and times of peak loggerhead sea turtle activity and have experimented with modifications to make their gear more robust. We field tested a new, lightweight, and inexpensive modification: self‐righting floats tethered to the inside of the crab pots. Thirty pairs of regular and modified pots were fished between 16 June and 31 July 2006. Damage by loggerhead sea turtles was found in 38% of all replicates, and blue crab catch was 57% lower in crab pots that had been discovered by loggerhead sea turtles. The float modification effectively reduced damage, but stronger effects were found when using plastic bait‐well covers that the crabbers had introduced. The modified pots were significantly less damaged (average damage index [ADI] = 1.38 with plastic covers and 2.01 with cardboard covers) than regular pots (ADI = 1.78 with plastic covers and 2.38 with cardboard covers). Average blue crab catch was significantly higher in pots with plastic bait‐well covers (15 crabs/modified pot, 18 crabs/regular pot) than in pots with cardboard covers (13 crabs/modified pot, 11 crabs/regular pot). However, there was a significant interaction of pot type with bait‐well cover type. When plastic covers were used, average blue crab catch was higher in regular pots (18 crabs/pot) than in modified pots (15 crabs/pot). The opposite case was observed when cardboard covers were used: catch was higher in modified pots (13 crabs/pot) than in regular pots (11 crabs/pot). A drawback to the float modification was a qualitative increase in pot drift and loss in high winds, resulting in the need for costly retrieval measures; crab pot loss may also jeopardize estuarine species that become trapped in derelict gear. Adopting these techniques, however, may help crabbers reduce gear damage, catch loss, and negative interactions with loggerhead sea turtles in this fishery.

Beach replenishment has been proposed to increase nesting habitat for horseshoe crabs, but its environmental consequences may compromise the egg development and viability of this declining species. Horseshoe crab habitat requirements were used to build a habitat suitability model in STELLA to predict the potential impacts of beach replenishment on horseshoe crab eggs. A habitat suitability index (H.S.I.) comprised of six variables (dissolved oxygen, sediment grain size, sand temperature, sand moisture, wave energy, and salinity) was developed and compared between replenished and natural beaches. Sediment grain size and dissolved oxygen were higher in the natural beach, whereas sand temperature and moisture were higher in the replenished beach, resulting in significantly higher suitability of the natural beach (p = 5.39 × 10 −15 , df = 30). The model was most sensitive to air temperature, rainfall, tide, and sediment grain size. This model is useful for understanding the processes affecting horseshoe crabs and predicting impacts of coastal management activities on habitat suitability. Based on the results of this model, beach replenishment is not recommended for increasing or improving horseshoe crab habitat, unless care is taken to match fill sediment to natural grain size and color.

North Carolina's fishery for the blue crab Callinectes sapidus is experiencing problems with gear damage during the summer season. Individuals of a protected species, the loggerhead sea turtle Caretta caretta, are the likely culprits of crab pot damage, bait theft, and reduced crab catch, perhaps with important economic impacts. In summer 2005, we conducted a fishing study in cooperation with a pair of crabbers operating one commercial blue crab boat in Core Sound, North Carolina, to characterize location, timing, and extent of damage to crab pots. We examined spatial and temporal overlap of fishing activity with loggerhead sea turtle sightings and quantified blue crab catch. Eighty‐seven percent of pots were damaged throughout the course of the study, and gear damage peaked in late June to early July. We measured a 40% reduction in blue crab catch in crab pots that were damaged. Loggerhead sea turtle sightings were consistent with areas of high gear damage. Our results should be considered by managers, who may be able to guide crabbers to concentrate fishing effort at times and areas of reduced overlap with loggerhead sea turtles so as to minimize damage.